Lead isotopes as a tool for gossan assessment in base metal exploration

Lead isotope measurements on gossans may be used as an exploration tool for Pb-Zn-Cu deposits of the “stratiform” type. The method is based on the homogeneous isotopic composition of stratiform orebodies and the close fit of their ratios to the so-called “growth curve”. These features also characterize oxidized outcrops. (gossans) of the primary sulphide ore. The retention of homogeneous Pb isotope ratios during oxidation was tested and proved for true gossans derived from known mineralization in which there was a variation in vertical depth from gossan to primary sulphide, different ages and different geological environments. The deposits included Pb-Zn-Cu (Woodlawn), Pb-Zn (Broken Hill), Zn-Pb (Dugald River), Zn-Cu-Pb (Currawang).The method has been extended to distinguish true gossans from false (pseudo) gossans where the base metals and associated trace elements have been scavenged from the surrounding rocks. It has also been applied to a company exploration program in which a number of ironstone cappings had been drilled and other geochemical information was available. Diamond drilling indicated that five prospects were barren, i.e. underlain by iron sulphides devoid of significant base metal mineralization. On the Pb isotope data, three of the prospects would be rejected; a fourth shows a particularly high potential and is worthy of further exploration, whilst the fifth initially showed high potential but a comparison of gossan and sulphide Pb isotope data after drilling suggests that the drill hole was sited on the fringes of economic mineralization.The Pb isotope method may be utilized further in exploration at the drilling stage. If sulphides are intersected, Pb isotopes may be used to distinguish barren sulphides from those with economic potential, even though they both may contain similar base metal concentrations.     

A method for automatic generation of the Recreation Opportunity Spectrum in New Zealand

The Recreation Opportunity Spectrum (ROS) has been used internationally as a tool to guide recreation planning. The spectrum as a map has primarily been generated manually and through digitisation by analysts with an in-depth knowledge of the region of interest. This paper seeks to outline an alternative method that is objective and repeatable to create a ROS map for New Zealand, using data from a variety of sources and manipulated with spatial tools available in a geographic information system. The result is a map that is consistent on a national scale, and a method that is repeatable. The model can be used to develop scenario modelling, change detection, and help guide management decisions.     

Groundwater assessment and management: implications and opportunities of globalization

The present and predicted increase in groundwater’s share of human freshwater withdrawals, its unprecedented importance for human activities globally, and the emerging threats from escalated and unplanned use and degradation, especially in the developing countries, point to the need for intensified efforts to cope with the imbalances. Despite these facts, there is little intervention by governments in developing countries. Sufficient knowledge, awareness and understanding of the groundwater resources and their proper management are missing in these countries, as well as in the international community. Links and trends are described, which highlight problem areas, such as water contamination, urbanization, and socio-economic factors related to groundwater management practices. Globalization provides novel opportunities for facilitating the process of acquiring and applying the necessary knowledge and can, and should, be further explored and developed. The likely benefits of this are: increase in convergence of understanding and approaches; the sharing of knowledge; and potentially wide-reaching, lasting, and scale-crossing networks. The international development and research community is in a particularly fortunate position to promote and facilitate such a process, which should go hand in hand with well focused and coordinated “on the ground” tasks, such as local networking, field investigations, capacity building, and advocacy activities.

Chronic oil pollution harms Magellanic penguins in the Southwest Atlantic

Petroleum pollution is a problem for seabirds along the Southwest Atlantic coast. Twenty-five groups from Salvador, Brazil (12 degrees 58'S) to San Antonio Oeste, Argentina (40 degrees 43'S) survey or rehabilitate sick or oiled seabirds. Four groups, one each in Brazil and Uruguay, and two in Argentina, kept counts of birds found alive and in need of rehabilitation. An average of 63.7% of the seabirds found were Magellanic penguins (Spheniscus magellanicus), with 3869 reported since 1987. Mainly adult penguins were found in Argentina (1605 of 2102 penguins of known age class) and Uruguay (158 of 197). Juveniles were most common in Brazil (234 of 325). Oil fouling was the most frequent cause of injury or sickness. The number of oiled penguins reported in their wintering range has greatly increased since the early 1990s and is strongly correlated with petroleum exports from Argentina. Our results show that chronic petroleum pollution is a problem for wildlife from Southern Brazil through Northern Argentina, and regulations and enforcement are failing to protect living resources.     

High-temperature hydrothermal alteration of the Boehls Butte anorthosite: origin of a bimodal plagioclase assemblage

The Boehls Butte anorthosite consists predominantly of an unusual bimodal assemblage of andesine and bytownite–anorthite. Oxygen isotope compositions of the anorthosite were profoundly altered by high temperature, retrograde interaction with meteoric-hydrothermal fluids that varied in composition from isotopically evolved to nearly pristine meteoric water. Oxygen isotope ratios of bulk plagioclase separates are in the range +7.0 to −6.2‰ V-SMOW, however, secondary ion mass spectrometry indicates spot-sized isotope values as low as −16‰. Typical inter- and intra-plagioclase grain variability is 3–6‰, and extreme heterogeneity of up to 20‰ is noted in a few samples. High-temperature hydrothermal alteration of intermediate plagioclase is proposed to explain the origin of bytownite–anorthite in the anorthosite and creation of its unusual bimodal plagioclase assemblage. The anorthite-forming reaction created retrograde reaction-enhanced permeability which, together with rapid decompression, extension, and unroofing of the anorthosite complex, helped to accommodated influx of significant volumes of meteoric-hydrothermal fluids into the anorthosite.     

‘We do not want to leave our land’: Pacific ambassadors at the United Nations resist the category of ‘climate refugees’

The issue of the social geographical dimensions of climate change is timely and important. This paper sets out to explore one example of this: how people living in the Pacific who are most at risk of being made landless by climate change are portrayed in policy discourse, and how high-level international representatives of Pacific nations have responded to these portrayals. At the heart of this is contention over the portrayal of Pacific Island peoples as ‘climate refugees’. This paper analyses a number of documents since the 1980s, largely from non-governmental organisations (NGOs) that deploy the identity construct of ‘climate refugees’. Fieldwork undertaken at the United Nations in New York in 2004 also enabled seven interviews with national ambassadors representing Pacific small island states. Interviews revealed how Pacific ambassadors have responded to the category of ‘climate refugees’, and positioned themselves in the discursive field surrounding the climate change debate. A poststructuralist framework, drawing on Foucault’s ideas of discourse and subject categories provided a means to critically scrutinise and better understand how people from Pacific countries are imagined in the wider, global geopolitical arena, but crucially, how leaders from these nations also construct themselves in relation to climate change and its associated impacts.     

The organic composition of Comet C/2001 A2 (LINEAR): I. Evidence for an unusual organic chemistry

We used the NIRSPEC instrument on the Keck-2 telescope atop Mauna Kea, HI to observe Comet C/2001 A2 (LINEAR) in a Target of Opportunity campaign on UT 2001 July 9.5, 10.5 August 4.4, 10.5. We measured seven organic parent volatiles (C₂H₆, C₂H₂, HCN, CH₄, CO, CH₃OH, H₂CO) simultaneously with H₂O. We obtained absolute production rates and relative abundances for parent volatiles, and also measured rotational temperatures for several of these species. The chemical composition of C/2001 A2 differs substantially from any comet we have observed to date. The abundances we measure (relative to H₂O) for C₂H₆, C₂H₂, HCN, and CH₃OH are enriched by a factor of ∼2 to 3 in C/2001 A2 compared with most comets in our database. Other molecular species were detected within the typical range of measured abundances. C/2001 A2 presented a unique opportunity to study the chemistry of a fragmenting comet where pristine areas are exposed to the Sun.     

Mid-21st century projections in temperature extremes in the southern Colorado Rocky Mountains from regional climate models

This study analyzes mid-21st century projections of daily surface air minimum (T_min) and maximum (T_max) temperatures, by season and elevation, over the southern range of the Colorado Rocky Mountains. The projections are from four regional climate models (RCMs) that are part of the North American Regional Climate Change Assessment Program (NARCCAP). All four RCMs project 2°C or higher increases in T_min and T_max for all seasons. However, there are much greater (>3°C) increases in T_max during summer at higher elevations and in T_min during winter at lower elevations. T_max increases during summer are associated with drying conditions. The models simulate large reductions in latent heat fluxes and increases in sensible heat fluxes that are, in part, caused by decreases in precipitation and soil moisture. T_min increases during winter are found to be associated with decreases in surface snow cover, and increases in soil moisture and atmospheric water vapor. The increased moistening of the soil and atmosphere facilitates a greater diurnal retention of the daytime solar energy in the land surface and amplifies the longwave heating of the land surface at night. We hypothesize that the presence of significant surface moisture fluxes can modify the effects of snow-albedo feedback and results in greater wintertime warming at night than during the day.     

The role of early formed structures on the development of the world class St Ives Goldfield,Yilgarn, WA

A revised structural interpretation for the Victory to Kambalda area of the world class St Ives Goldfield in the Archean Yilgarn Craton has mapped out the distribution of WNW-trending faults within this area of the field. These previously cryptic WNW-trending structures had been identified in gravity data, and also by isopach thickness variations. The WNW-trending faults acted as transfers syn-gold mineralization, although only discrete segments of these faults were active during the main stage of gold mineralization. Where mineralized, the faults transferred strain from a complex combination of block-on-block movement associated with thrusting and strike-slip movement on NW- and N-trending faults. Along some segments N-trending mineralized faults terminate against the WNW-trending faults. Many of the WNW-trending faults correlate with major strike changes on regional and camp-scale faults and they are domain boundaries for the critical N-trending fault segments that host high-grade gold within contractional jogs. The WNW-trending faults also show evidence for an older deformation history prior to main-stage gold, which may extend back to early basin development associated with ultramafic and mafic volcanism. They are inferred to have been a series of early WNW-trending normal faults and breached relay ramps associated with oblique rifting along an older NNW-trending basement boundary.